This section is from the book "An Experimental History Of The Materia Medica", by William Lewis.
Olea fativa C. B. Olea europaea Linn. Olive: an evergreen tree, with oblong, narrow, willow-like leaves, and monopetalous whitish flowers, cut into four sections, followed by clusters of oval black fruit, containing, under a fleshy pulp, a hard rough stone. It is a native of the southern parts of Europe, and bears the ordinary winters of our own climate.
The fruit of this tree (oliva) has a bitter, austere, very disagreeable taste: pickled, as brought from abroad, it proves les ungrateful, and is supposed to promote appetite and diges-tion, and attenuate viscid phlegm in the first passages: the Lucca olives, which are smaller than the others, have the weakest taste; and the Spanish, or larger, the strongest: those brought from Provence, which are of a middling size, are in general most esteemed. But the principal consumption of olives is in the preparation of the common sallad oil (oleum olivarum Pharm. Lond. & Edinb.) which is obtained by grinding and pressing them when thoroughly ripe: the finer and purer oil issues first by gentle pressure; and inferiour sorts, on heating the residuum and pressing it more strongly. All these oils contain a portion of watery moisture; and of the mucilaginous substance of the fruit: to separate these, and thus prevent the oil from growing rancid, some sea salt is added, which not being dissoluble in the pure oil, imbibes the watery and mucilaginous parts, and finks with them to the bottom. As this oil grows thick in a moderate degree of cold, a part of the salt, thrown up by shaking the vessel, is sometimes detained in it, so as to render the taste senfibly saline. In virtue, it does not differ materially from the other flavourless expressed oils: it is preferred to the others for dietetic uses, and in plasters and unguents, but is more rarely employed as an internal medicine.